Methods and compositions for controlled release of amine, alcohol and thiol drugs, e.g., narcotic analgesics, and tricyclic amine antidepressants, are provided. The drug is releasably covalently bonded to a polymer or other activity-blocking moiety. Release is by an unmasking reaction resulting in the formation of a chemical group that undergoes a second reaction releasing the drug. For example, the narcotic analgesic fentanyl covalently attached to an inert polymer by way of its nitrogen through formation of a quaternary vinylammonium salt is released by hydrolysis of an acetal exposing an alcohol that undergoes an intramolecular nucleophilic substitution reaction involving displacement of the fentanyl nitrogen. Process rate is controlled by controlling the rate of the intramolecular substitution reaction through varying the number of atoms in the chain connecting the alcohol group and the vinylic carbon and/or by the addition of substituents on that chain, and/or by the acetal hydrolysis rate.
